JP2006182829A - Optical polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical polyester film having good optical performance, wherein when the film is used as a member for an LCD, a PDP, an organic EL, a projection display and the like, it has no unevenness and defects, achieves high luminosity and can provide high-quality images. <P>SOLUTION: A biaxially oriented optical polyester film is composed of a polyester, has a film haze of 5% or less, and has a birefringence (Δn) of 0.02 or more. The deflection of the Δn in any square having a side of 100 mm in the film plane is 0.010 or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical polyester film, and more specifically, various optical members used for a liquid crystal display (hereinafter abbreviated as LCD), a plasma display (hereinafter abbreviated as PDP), and the like, The present invention relates to a polyester film used for a protective film, a release film, etc. used in the manufacturing process of the above-mentioned product, which is excellent in optical characteristics and can contribute to improvement in quality of optical products and reduction in energy consumption. .

  Conventionally, polyester films, especially biaxially stretched films of polyethylene terephthalate and polyethylene naphthalate, have excellent mechanical properties, heat resistance, and chemical resistance. Magnetic tape, ferromagnetic thin film tape, photographic film, packaging It is widely used as a material for films, films for electronic parts, electrical insulation films, metal laminate films, films to be attached to glass surfaces such as glass displays, and protective films for various members.

  In recent years, polyester films have been widely used for various optical films, in particular, prism films for LCD members, light diffusion sheets, reflectors, touch panels, and other base films, antireflection base films, display explosion-proof base films, and PDPs. It is used for various applications such as filter films. In these optical products, in order to obtain a bright and clear image, the base film used as an optical film has good transparency from its usage, and there are no defects such as foreign matter and scratches that affect the image. Necessary. In addition, it is necessary for obtaining an image having no unevenness even when polarized light is used, in particular, that there is no retardation unevenness due to uneven orientation of the polymer and uneven thickness.

  The polyester film is usually obtained by subjecting an amorphous sheet obtained by melt extrusion to a sheet shape and rapid cooling and solidification in the longitudinal direction and the transverse direction, followed by heat treatment. If the uniformity of cooling and stretching is not sufficient in these steps, the above-mentioned retardation unevenness remains, and there is a problem that the image is deteriorated when used for optics.

Brightness is an important characteristic in displays, and it is known that the polyester film used as a member affects the brightness. In particular, when a high-quality image is obtained, a high brightness is required. Therefore, the polyester film has been required to have a characteristic for realizing a high brightness. For this purpose, it goes without saying that the polyester film has a high degree of transparency, but in addition to this, it is necessary to have further optically advantageous properties.
JP 2003-201357 A

  The present invention has been made in view of the above circumstances, and its solution is to achieve high brightness without unevenness and defects when used as a member for LCD, PDP, organic EL, projection display, etc. An object of the present invention is to provide a polyester film having good optical performance and capable of giving a high-quality image.

  That is, the gist of the present invention is a film made of polyester, having a film haze of 5% or less, a birefringence (Δn) of 0.02 or more, and a square having an arbitrary side of 100 mm in the film plane. The biaxially oriented polyester film for optics is characterized in that the fluctuation of Δn is 0.010 or less.

Hereinafter, the present invention will be described in more detail.
The polyester used for the polyester film in the present invention refers to a polyester obtained by polycondensation of an aromatic dicarboxylic acid and an aliphatic glycol. Examples of the aromatic dicarboxylic acid include terephthalic acid and 2,6-naphthalenedicarboxylic acid, and examples of the aliphatic glycol include ethylene glycol, diethylene glycol, and 1,4-cyclohexanedimethanol. Representative polyesters include polyethylene terephthalate (PET), polyethylene-2,6-naphthalenedicarboxylate (PEN), and the like. In the present invention, it is necessary to contain 2.0 to 10.0 mol% of a third component other than the main constituent, preferably 2.5 to 10 mol%, more preferably 3.0 to 8.0. Mol%.

As a method for containing the third component, a copolymer polyester containing a predetermined amount of a copolymer component as a raw material for producing a film may be used, or a copolymer polyester containing a copolymer component larger than a predetermined amount. Further, a raw material obtained by blending a copolymer polyester or homopolyester having a small content of the copolymer component may be used.
Examples of the third component herein include isophthalic acid, phthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid, sebacic acid and the like as the dicarboxylic acid component, and P-oxybenzoic acid as the oxycarboxylic acid. Examples of the glycol component include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, and the like. Among these, when diethylene glycol, triethylene glycol, or 1,4-cyclohexanedimethanol is used, the optical unevenness of the film due to the orientation and thickness unevenness of the polymer can be efficiently reduced, and the flatness of the film and This is preferable in that heat resistance and dimensional stability can be maintained at a high level. Here, as a third component contained in the polyester, diethylene glycol by-produced from ethylene glycol during polymerization is also included.

  The polyester in the present invention is a conventionally known method, for example, a method of directly obtaining a low-polymerization degree polyester by reaction of a dicarboxylic acid and a diol, or a lower alkyl ester of a dicarboxylic acid and a diol reacted with a conventionally known transesterification catalyst. Then, it can obtain by the method of performing a polymerization reaction in presence of a polymerization catalyst. As the polymerization catalyst, a known catalyst such as an antimony compound, a germanium compound, or a titanium compound may be used. Preferably, the amount of the antimony compound is zero or 100% or less as antimony to reduce the dullness of the film. .

  The polyester may be chipped after melt polymerization, and further subjected to solid phase polymerization as necessary under heating under reduced pressure or in an inert gas stream such as nitrogen. The intrinsic viscosity of the obtained polyester is preferably 0.40 dl / g or more, and preferably 0.40 to 0.90 dl / g.

  You may mix | blend particle | grains in the polyester layer in this invention with the main objective of providing lubricity. The kind of the particle to be blended is not particularly limited as long as it is a particle capable of imparting slipperiness. Specific examples thereof include silica, calcium carbonate, magnesium carbonate, barium carbonate, calcium sulfate, calcium phosphate, and phosphoric acid. Examples thereof include particles of magnesium silicon oxide, kaolin, aluminum oxide, titanium oxide and the like. Further, the heat-resistant organic particles described in JP-B-59-5216, JP-A-59-217755 and the like may be used. Examples of other heat-resistant organic particles include thermosetting urea resins, thermosetting phenol resins, thermosetting epoxy resins, benzoguanamine resins, and the like. Furthermore, precipitated particles obtained by precipitating and finely dispersing a part of a metal compound such as a catalyst during the polyester production process can also be used.

  On the other hand, the shape of the particles to be used is not particularly limited, and any of a spherical shape, a block shape, a rod shape, a flat shape, and the like may be used. Moreover, there is no restriction | limiting in particular also about the hardness, specific gravity, a color, etc. These series of particles may be used in combination of two or more as required.

  Further, the average particle size of the particles used is usually preferably 0.01 to 5 μm. If the average particle size is less than 0.01 μm, the particles tend to aggregate and the dispersibility may be insufficient. On the other hand, if the average particle size exceeds 5 μm, the surface roughness of the film becomes too rough and transparent. It will become inferior.

  Further, the particle content in the polyester is usually in the range of 0.0003 to 1.0% by weight, preferably 0.0005 to 0.5% by weight, based on the total polyester constituting the film. When the particle content is less than 0.0003 wt%, the slipperiness of the film may be insufficient. On the other hand, when the content exceeds 1.0 wt%, the transparency of the film is insufficient. There are cases.

  The method for adding particles to the polyester is not particularly limited, and a conventionally known method can be adopted. For example, it can be added at any stage for producing the polyester, but the polycondensation reaction may proceed preferably after the esterification stage or after the transesterification reaction. Also, a method of blending a slurry of particles dispersed in ethylene glycol or water with a vented kneading extruder and a polyester raw material, or a blending of dried particles and a polyester raw material using a kneading extruder. It is done by methods.

  In addition to the above-mentioned particles, conventionally known antioxidants, heat stabilizers, lubricants, antistatic agents, fluorescent brighteners, dyes, pigments, and the like are added to the polyester film in the present invention as necessary. be able to. Depending on the use, an ultraviolet absorber, particularly a benzoxazinone-based ultraviolet absorber, may be contained.

  The thickness of the polyester film of the present invention is not particularly limited as long as it can be formed as a film, but is usually 9 to 300 μm, preferably 20 to 250 μm, and more preferably 25 to 200 μm.

  The film of the present invention has a film haze of 5% or less, preferably 2.5% or less, more preferably 1.2% or less, and particularly preferably 1.0% or less. The film of the present invention is widely used for optical applications because of its excellent transparency. However, when the film haze exceeds 5%, it is unsuitable for optical use.

  The film of the present invention has a birefringence (hereinafter Δn) of 0.02 to 0.10, preferably 0.02 to 0.08, and more preferably 0.03 to 0.07. When Δn is 0.02 or less, when the film of the present invention is sandwiched between polarizing plates and light is passed through, depending on the angle of the polarizing plate, strong red is likely to be developed, and the color tone of the liquid crystal screen may be significantly deteriorated. is there. On the other hand, film forming conditions where Δn exceeds 0.10 are inappropriate for optical use due to problems such as increased heat shrinkage.

  Further, the film of the present invention has a Δn runout of 0.010 or less, preferably 0.008 or less, in a square with an arbitrary side of 100 mm in the film plane. When the fluctuation of Δn exceeds 0.010, when the film of the present invention is sandwiched between polarizing plates and light is passed through, significant color unevenness occurs depending on the angle of the polarizing plates, and the color tone of the liquid crystal screen is significantly deteriorated. There is a fear.

  The polyester film for optical use of the present invention, particularly for display, has a color tone b * value measured by a single transmission method of preferably -5 to +3, more preferably -4 to +2, particularly preferably -3. The range is 5 to +1. When the b * value exceeds +3, it is often inappropriate because the color tone of the image becomes inferior or the luminance becomes low when used for a display because of its strong yellowishness. On the other hand, although there is a problem of color tone in a film lower than -5, since a b * value is not lower than -5 in a normal polyester film, a method such as using an additive is used. However, it is not preferable because it may cause problems such as bleeding out of the additive and reliability during long-term use. In order to obtain a film having such a color tone, the catalyst and auxiliary agent for producing the raw material polyester are selected, the amount of the catalyst is reduced as much as possible, and the polyester is heated to an unnecessarily high temperature during polymerization and film formation. Further, it is possible to adopt methods such as preventing the melting time from becoming longer and reducing the amount of the recycled raw material.

In the film of the present invention, the sum of the front and back surfaces of the oligomer (cyclic trimer) deposited on the film surface after heat treatment at 180 ° C. for 10 minutes is preferably 15 mg / m ² or less, more preferably 10 .0mg / ^{m 2,} particularly preferably not more than 8.0 mg / ^{m 2.} When the amount of oligomer deposition on the film surface exceeds 15 mg / m ² , the oligomer crystallizes on the surface and lowers the transparency of the film, or dissolves in the functional layer provided on the film and affects the properties. It is easy to cause problems such as.

  In order to make the oligomer precipitation amount on the film surface by heat treatment within the above range, it is particularly a laminated film composed of at least three layers by coextrusion, and a polyester having a low oligomer content is used as the outermost layer constituting the surface layer, By providing the coating layer inline / offline, the oligomer deposition amount on the film surface after the heat treatment can be controlled within the above range by suppressing oligomer precipitation on the film surface.

  The film of the present invention can be formed into a laminated structure using a co-extrusion method. In this case, the outermost layer thickness is a thickness of only one side, preferably 3 μm or more, more preferably 5 μm or more and 1 of the total thickness. / 4 or less, more preferably 1/5 or less, and particularly preferably 1/10 or less. When the thickness is less than 3 μm, oligomers (cyclic trimers) contained in the inner layer are deposited on the film surface due to heat history during processing, etc., and contamination of the production line and an increase in the amount of foreign matter on the film surface are observed. On the other hand, if it is thicker than 1/4 of the total thickness, the amount of particles to be blended in the outermost layer may increase and the transparency may be impaired.

  On the other hand, when carrying out by a single layer, it is also preferable to make a film not contain particle | grains as much as possible, and to make a coating layer of front and back contain particle | grains.

  When it manufactures as this laminated | multilayer film, content of the 3rd component in this invention needs to make the amount of 3rd component contained in the whole film with respect to polyester of the whole film into the above-mentioned range. This is because the prevention of optical unevenness, which is a problem to be improved in the present invention, relates to the transmitted light of the film and relates not only to the film surface and the inside but also to the entire characteristics.

  Moreover, when adding additives, such as the said ultraviolet absorber and dye, it is preferable to mix | blend with the intermediate | middle layer of a laminated | multilayer film.

  Hereinafter, although the manufacturing method of the polyester film of this invention is demonstrated concretely, as long as the summary of this invention is satisfied, this invention is not specifically limited to the following illustrations.

  First, a dried or undried polyester chip by a known method is supplied to a melt extrusion apparatus and heated to a temperature equal to or higher than the melting point of each polymer and melted. Next, the molten polymer is extruded from a die and rapidly cooled and solidified on a rotary cooling drum so that the temperature is equal to or lower than the glass transition temperature to obtain a substantially amorphous unoriented sheet. In this case, in order to improve the flatness of the sheet, it is preferable to improve the adhesion between the sheet and the rotary cooling drum. In the present invention, an electrostatic application adhesion method and / or a liquid application adhesion method is preferably employed.

  In the present invention, the sheet thus obtained is stretched biaxially to form a film. Specifically describing the stretching conditions, the unstretched sheet is preferably stretched 2 to 6 times at 70 to 145 ° C. in the longitudinal direction to form a longitudinal uniaxially stretched film, and then at 90 to 160 ° C. in the lateral direction. It is preferable to perform 2-6 times stretching and to heat-process at 150-240 degreeC for 1 to 600 seconds. Further, at this time, a method of relaxing 0.1 to 20% in the longitudinal direction and / or the transverse direction in the maximum temperature zone of the heat treatment and / or the cooling zone at the heat treatment outlet is preferable. Further, it is possible to add re-longitudinal stretching and re-lateral stretching as necessary.

  In the present invention, as described above, two or three or more polyester melt extruders can be used to form a laminated film of two layers or three or more layers by a so-called coextrusion method. As the layer structure, an A / B structure using an A raw material and a B raw material, or an A / B / A structure, and further using a C raw material to form an A / B / C structure or other film. Can do. For example, the surface shape of the A layer can be designed using specific particles as the A raw material, and a film having an A / B or A / B / A structure can be formed using a raw material not containing particles as the B raw material. In this case, since the raw material of B layer can be selected freely, a cost advantage etc. are large. Further, even if the recycled material of the film is blended with the B layer, the surface roughness can be designed by the surface A layer, so that the cost advantage is further increased.

  In particular, since the film of the present invention is used for optical applications, a hard coat layer, an antireflection layer, an antiglare layer, or the like is provided, or a vapor deposition layer or the like is provided. A coating layer as an undercoat layer can be provided for the purpose of improving adhesion or preventing charging in order to keep the surface clean. In forming such a coating layer, the method of forming a film, in particular, after stretching in the longitudinal direction and before stretching in the lateral direction can form a very thin coating layer, and the coating solution drying and curing reaction Is preferable in that it can be carried out in the film forming process. The coating layer is preferably a combination of a crosslinking agent and various binder resins, and as the binder resin, a polymer selected from polyester, acrylic polymer and polyurethane is usually employed from the viewpoint of adhesiveness. Each of the above polymers shall also include derivatives thereof. The derivative here refers to a polymer obtained by reacting a reactive compound with a copolymer or a functional group with another polymer.

  If necessary, the film may be coated with an off-line coat after production. Moreover, it does not matter on one side or both sides. The coating material may be either water-based and / or solvent-based for offline coating, but is preferably water-based or water-dispersed for in-line coating.

  In addition, since the film of the present invention is used for optics, it is also preferable to form a functional multilayer thin film for the purpose of preventing dust reflection due to reflection of external light and static electricity, as well as electromagnetic shielding, in addition to improving adhesiveness. .

  Among the polyesters, acrylic polymers, and polyurethanes that are used as coating agents in the present invention, particularly preferred polymers have a glass transition temperature (Tg) of 0 ° C. or higher, more preferably 40 ° C. or higher. It is a polyurethane having a carboxylic acid residue, at least a part of which is made water-based using an amine or ammonia.

  As the crosslinking agent resin, melamine-based, epoxy-based, and oxazoline-based resins are generally used, but melamine-based resins are particularly preferable from the viewpoints of coatability and durable adhesiveness. The melamine-based resin may be either a monomer, a condensate composed of a dimer or higher multimer, or a mixture thereof.

  In the present invention, it is preferable to contain inorganic particles or organic particles in the coating layer in order to further improve the slipperiness, adhesion and the like. The amount of the particles in the coating agent is usually 0.5 to 10% by weight, preferably 1 to 5% by weight. When the blending amount is less than 0.5% by weight, the blocking resistance may be insufficient. When the blending amount exceeds 10% by weight, the transparency of the film is hindered and the sharpness of the image tends to be lowered.

  Examples of the inorganic particles include silicon dioxide, alumina, zirconium oxide, kaolin, talc, calcium carbonate, titanium oxide, barium oxide, carbon black, molybdenum sulfide, and antimony oxide. Among these, silicon dioxide is easy to use because it is inexpensive and has various particle sizes. On the other hand, examples of the organic particles include polystyrene or polyacrylate polymethacrylate in which a crosslinked structure is achieved by a compound containing two or more carbon-carbon double bonds in one molecule (for example, divinylbenzene).

  The above inorganic particles and organic particles may be surface-treated. Examples of the surface treatment agent include a surfactant, a polymer as a dispersant, a silane coupling agent, a titanium coupling agent, and the like. The content of the particles in the coating layer is preferably 10% by weight or less, more preferably 5% by weight or less as an appropriate addition amount that does not impair the transparency.

  Further, the coating layer may contain an antistatic agent, an antifoaming agent, a coating property improving agent, a thickener, an antioxidant, an ultraviolet absorber, a foaming agent, a dye, a pigment, and the like.

  As long as water is the main medium, the coating agent may contain a small amount of an organic solvent for the purpose of improving dispersion in water or improving the film-forming performance. It is necessary to use the organic solvent as long as it is soluble in water. Examples of the organic solvent include aliphatic or alicyclic alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl alcohol, ethyl alcohol, and methyl alcohol, glycols such as propylene glycol, ethylene glycol, and diethylene glycol, n-butyl cellosolve, Glycol derivatives such as ethyl cellosolve, methyl cellosolve, propylene glycol monomethyl ether, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate and amyl acetate, ketones such as methyl ethyl ketone and acetone, amides such as N-methylpyrrolidone Can be mentioned. These organic solvents may be used in combination of two or more as required.

  As a coating method of the coating agent, for example, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater or other coating apparatus as shown in Yuji Harasaki, Tsuji Shoten, published in 1979, “Coating Method” Can be used.

  The coating layer may be formed only on one side of the polyester film or on both sides. When formed only on one side, other characteristics can be imparted by forming a coating layer different from the above-mentioned coating layer on the opposite surface as necessary. In addition, in order to improve the applicability | paintability and adhesiveness to the film of a coating agent, you may give a chemical process and an electrical discharge process to a film before application | coating. Further, in order to further improve the surface characteristics, a discharge treatment may be performed after the coating layer is formed.

The thickness of the coating layer is usually 0.01 to 0.5 μm, preferably 0.015 to 0.3 μm as the final dry thickness. When the thickness of the coating layer is less than 0.01 μm, the effect of the present invention may not be sufficiently exhibited. When the thickness of the coating layer exceeds 0.5 μm, the films tend to stick to each other, and particularly when the coated film is re-stretched to increase the strength of the film, it adheres to the roll in the process. There is a tendency to become easy. The above-mentioned problem of sticking appears particularly when the same coating layer is formed on both sides of the film. When such a coating film is applied to optical applications, the coating layer surface is not coated. This is a problem when an antireflection layer or the like is further provided on the surface of the substrate. The reason for the occurrence of coating leakage is not clear, but foreign matter in the film creates coarse protrusions on the surface of the film, which acts as a core and the coating agent repels and stretches to cause coating leakage or the film surface. It is conceivable that the oligomer or dust adhering to the core becomes a nucleus and the coating agent repels and disappears from the nucleus. Therefore, it is necessary to form a film under such a condition that dust and foreign matters that can become nuclei are removed as much as possible. Such foreign substances include oligomers adhered or deposited on the film, so that reducing the amount of oligomers contained in the film has the effect of reducing the amount of coating.

When the film of the present invention thus obtained has a coating layer, the number of coating spots is preferably 50 or less, more preferably 30 or less, and particularly preferably 10 or less per 10 m ^{2 of} film. In any case, in an optical film that will become more and more severe in the future, it is necessary to make coating coating as zero as possible.

  The film of the present invention exerts particularly excellent effects when used for optics, and as specific members thereof, a reflector for a backlight for a liquid crystal display, a diffuser, a prism sheet, Lens sheets, brightness enhancement films, protective films for liquid crystal panels, release films for processes during panel manufacturing, and so-called PDP filters for plasma displays, electromagnetic shielding, near infrared shielding, color correction, ultraviolet shielding Effectively used as a substrate that requires a high degree of transparency, such as a film substrate having various functions such as antireflection, and a process for manufacturing a panel, and an image forming screen for a projection television. Is done.

  The film of the present invention is excellent in optical properties such as transparency, low haze, and optical uniformity, can contribute to improving the quality of optical products and reducing energy consumption, and is used for various types of LCDs, PDPs, etc. When used as an optical member, its advanced characteristics are exhibited and its industrial value is extremely high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measuring method used in the present invention is as follows.

(1) Measurement of Intrinsic Viscosity of Polyester 1 g of polyester was accurately weighed and dissolved by adding 100 ml of a mixed solvent of phenol / tetrachloroethane = 50/50 (weight ratio), and measured at 30 ° C.

(2) Measurement of third component (copolymerization component) content About a solution in which a resin sample was dissolved in a deuterated chloroform / hexafluoroisopropanol (weight ratio 7/3) mixed solvent to a concentration of 3% by weight, Using a nuclear magnetic resonance apparatus (“JNM-EX270 type” manufactured by JEOL Ltd.), 1 H-NMR was measured to assign each peak, and the content of the copolymer component was calculated from the integrated value of the peak.

(3) Measurement of average particle size (d ₅₀ : μm) Integration (weight basis) 50% in equivalent spherical distribution measured using centrifugal sedimentation type particle size distribution measuring device (SA-CP3 type manufactured by Shimadzu Corporation) Was the average particle size.

(4) Film haze Film haze was measured with an integrating sphere turbidimeter “NDH-300A” manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS-K-7105.

(5) Measurement of birefringence (Δn) Using an Abbe refractometer manufactured by Atago Co., Ltd., using a sodium lamp as the light source, the refractive index of the film is measured, and the birefringence (Δn) is calculated by the following equation. did.
Δn = nγ−nβ
In the above formula, nγ and nβ each represent the maximum refractive index in the plane of the film and the refractive index in the plane of the film perpendicular thereto.

(6) Measurement of Δn shake A sample with a square size of 100 mm on a side is cut out at an arbitrary position in the film plane, and when a straight line is drawn in a lattice pattern at intervals of 25 mm in the square, it corresponds to the intersection. The difference between the maximum value and the minimum value among the 16 measured values obtained by measuring Δn according to the item (5) in the part (16 points in total) was defined as Δn shake.

(7) Suitability of optical member-luminance As a representative of the optical member, characteristics when used as a diffusion plate were evaluated. That is, an acrylic binder containing particles was applied to one side of the film to form a light diffusion layer. The obtained diffusion sheet was incorporated into a backlight unit, and the quality of the obtained planar light emission was evaluated from the following viewpoints.
Luminance level (evaluated using a luminance meter and compared with the case of using the film of Comparative Example 1)
A: Brightness was improved and improvement was observed.
B: Decrease in luminance cannot be confirmed and usable level C: Decrease in luminance

(8) Optical member suitability—polarization unevenness A film was sandwiched between polarizing plates, and the quality and color tone were observed on the backlight unit from the following viewpoints. The angle between the polarizing plates was such that the film color tone was most clear.
A: Strong red part cannot be confirmed and color unevenness is hardly seen B: Strong red part can be confirmed partially or color unevenness is slightly seen but practically usable C: Strong red part can be confirmed on the entire surface or color tone Unevenness is significant and affects the image on the LCD screen.

The production method of the polyester used in the following examples is as follows.
<Manufacture of polyester>
<Method for producing polyester (A)>
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After 0.04 part of ethyl acid phosphate was added to this reaction mixture, 0.03 part of antimony trioxide was added and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.68 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The obtained polyester (A) had an intrinsic viscosity of 0.68 and a diethylene glycol content of 1.0 mol%.

<Method for producing polyester (B)>
In the method for producing polyester (A), after adding 0.04 part of ethyl acid phosphate, 0.4 part of silica particles having an average particle diameter of 2.2 μm dispersed in ethylene glycol and 0.03 part of antimony trioxide are added. In addition, polyester (B) was obtained using the same method as the production method of polyester (A) except that the polycondensation reaction was stopped at the time corresponding to the intrinsic viscosity of 0.66. The obtained polyester (B) had an intrinsic viscosity of 0.66 and a diethylene glycol content of 1.0 mol%.

<Method for producing polyester (C)>
In the method for producing polyester (A), the starting material is 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 2 parts by weight of diethylene glycol, and the method for producing polyester (A) is used except that germanium oxide is used as a polymerization catalyst. A polyester (C) was obtained using the same method as described above. In addition, the addition method of germanium oxide employ | adopted the well-known method, The addition amount was 100 ppm with respect to the raw material weight as germanium. The obtained polyester (C) had an intrinsic viscosity of 0.68, and the diethylene glycol content in the polymer was 4.0 mol%.

<Method for producing polyester (D)>
The starting material is 100 parts by weight of dimethyl terephthalate, 54 parts by weight of ethylene glycol and 25 parts by weight of 1,4-cyclohexanedimethanol, 0.011 part by weight of tetrabutoxy titanate is used as a catalyst, and the reaction start temperature is 150 ° C. The reaction temperature was gradually increased with the distillation of methanol, and the temperature was raised to 230 ° C. after 3 hours, and the reaction was continued for another hour. Thereafter, the temperature of the reaction product was gradually raised from 230 ° C., and the pressure was gradually reduced from the normal pressure, and finally the temperature was 280 ° C. and the pressure was 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.70 due to a change in stirring power of the reaction vessel, and the polymer was discharged under nitrogen pressure. The intrinsic viscosity of the obtained polyester (D) was 0.70, the content of 1,4-cyclohexanedimethanol was 33 mol%, and the content of diethylene glycol was 1.0 mol%.

<Method for producing polyester (E)>
In the production method of the polyester (A), the polyester (E) is produced using the same method as the production method of the polyester (A) except that the starting dicarboxylic acid is 80 parts by weight of dimethyl terephthalate and 20 parts of isophthalic acid. Obtained. The obtained polyester (E) had an intrinsic viscosity of 0.67 and a content of diethylene glycol of 1.0 mol%.

<Manufacture of polyester film>
Two vents using the above-mentioned polyester (B) and (C) mixed at a ratio of 12% and 88%, respectively, as the raw material for the A layer and 100% of the polyester (C) as the raw material for the B layer. Each is supplied to a twin screw extruder and melted at 285 ° C., and each layer is composed of two layers and three layers (A / B / A) with the A layer as the outermost layer (surface layer) and the B layer as the intermediate layer. The sheet was extruded and extruded from the die, and cooled and solidified on a cooling roll having a surface temperature set to 40 ° C. using an electrostatic application adhesion method to obtain an unstretched sheet. Next, the film was stretched 3.3 times in the machine direction at a film temperature of 85 ° C. by utilizing the difference in peripheral speed of the roll, and after applying a coating agent having the composition shown below, it was led to a tenter and 3. The film was stretched 6 times, heat treated at 230 ° C., and then relaxed 2% in the transverse direction to obtain a laminated polyester film having a thickness of 188 μm. The thickness of each layer of the obtained film was 10/168/10 μm. The thickness of the coating layer was 0.08 μm.

(Coating agent composition: weight ratio)
a / b / c / d = 47/20/30/3
Here, a is a polyester dispersion of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / ethylene glycol / diethylene glycol / triethylene glycol = 31/16/3/22/21 (molar ratio) b is methyl methacrylate / Ethyl acrylate / acrylonitrile / N-methylol methacrylamide = 45/45/5/5 (molar ratio) emulsion polymer (emulsifier: anionic surfactant)
c is hexamethoxymethylmelamine (melamine-based crosslinking agent)
d is an aqueous dispersion (inorganic particles) of silicon oxide having a particle size of 0.06 μm.
It is.

  In Example 1, the raw material of the B layer is a raw material in which the polyesters (B) and (C) are mixed at a ratio of 4% and 96%, respectively, the thickness of each layer is 10/105/10 μm, and the film forming conditions are stretching. The magnification was 3.0 times in the vertical direction and 3.6 times in the horizontal direction, and the coating conditions were the same as in Example 1 to obtain a 125 μm thick polyester film.

  In Example 1, the raw material of the B layer is a raw material obtained by mixing polyester (D) and (C) at a ratio of 5% and 95%, respectively, and the A layer is polyester (B), (C), and (D), respectively. The raw materials were mixed at a ratio of 12%, 83% and 5%, and the draw ratio was 3.3 times in the vertical direction and 4.0 times in the horizontal direction, and the thickness of each layer was 5/90/5. A polyester film having a thickness of 100 μm was obtained in the same manner as Example 1 except for the above.

  In Example 3, the raw material of the B layer is a raw material in which the polyesters (D) and (C) are mixed at a ratio of 35% and 65%, respectively, and the A layer is the polyester (B), (C), and (D), respectively. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 3 except that the raw materials were mixed at a ratio of 12%, 53%, and 35%. Since the obtained film has too much content of the third component, when compared with the films of Examples 1 to 3, when used as an optical film, its properties are deteriorated and the heat resistance is insufficient. There was also a lack in maintaining the flatness of the film at the time.

  The raw material of the B layer is a raw material obtained by mixing polyester (E) and (C) at a ratio of 10% and 90%, respectively. The A layer is 12% and 78% of the polyester (B), (C), and (E), respectively. A polyester film having a thickness of 188 μm was prepared in the same manner as in Example 1 except that the raw material was mixed at a ratio of 10%, and the draw ratio was 3.0 times in the longitudinal direction and 4.0 times in the transverse direction. Obtained.

(Comparative Example 1)
A mixed raw material in which polyesters (B) and (A) were mixed at a ratio of 12% and 88%, respectively, was used as the raw material for the A layer, and a raw material of 100% polyester (A) was used as the raw material for the B layer. A polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the direction was 3.3 times and the horizontal direction was 3.3 times.

(Comparative Example 2)
A single layer polyester film using one extruder was prepared using raw materials in which polyesters (B) and (C) were mixed in proportions of 30% and 70%, respectively. The film forming conditions were the same as in Example 1 except that the film was a single layer, and the film thickness was 188 μm.

(Comparative Example 3)
In Example 1, a polyester film having a thickness of 188 μm was obtained in the same manner as in Example 1 except that the draw ratio was 2.5 times in the vertical direction and 3.3 times in the horizontal direction.
The physical properties and optical member suitability of the obtained film are summarized in Table 1. It can be seen that a film satisfying the requirements of the present invention has high suitability for optical use.

  In the above table, DEG means diethylene glycol, 1,4-CHDM means 1,4-cyclohexanedimethanol, IPA means isophthalic acid, and the third component content in Examples 3 to 5 includes DEG.

The film of the present invention can be suitably used for, for example, various optical members used for LCDs, PDPs, and the like, and protective films and release films used in the manufacturing process of products in the optical field.

Claims (1)

A film made of polyester, having a film haze of 5% or less, a birefringence (Δn) of 0.02 or more, and a Δn runout in a square of 100 mm on any side in the film plane is 0. A biaxially oriented polyester film for optical use, characterized in that it is .010 or less.